a. Field of the Invention
The present invention pertains generally to electrical devices and more specifically to bandgap current and voltage reference circuits.
b. Description of the Background
Reference circuits are needed to bias electronic circuits. Reference sources of electronic circuits use the conduction and valence band difference of the intrinsic substrate material (silicon) to generate a reference voltage or current which may vary as a result of process variations or variations in environmental temperatures. The negative temperature coefficient of the silicon bandgap voltage is cancelled in prior art circuits by using the positive temperature coefficient of thermal voltage to generate the reference source. Typically, low temperature coefficient poly resistors, i.e., on the order of 6×10−4, are used to generate a reference source. However, these poly resistors have low sheet resistance, i.e., on the order of 30-40 ohms per square, and as such, consume a large amount of space on the die. In many cases, the poly resistors may consume up to 50 percent of the die space. In addition, poly resistors have large process variations, and many times require expensive laser trimming to provide the needed accuracy that is not available because of process variations.